Scanning Tunneling Microscope In The Name of Allah Scanning Tunneling Microscope Pooria Gill PhD of Nanobiotechnology pooriagill@yahoo.com

Image from an STM Iron atoms on the surface of Cu(111)

Microscopy Optical Microscopy Scanning Electron Microscopy Scanning Probe Microscopy

Scanning Probe Microscope Atomic Force Microscope (AFM) Electrostatic Force Microscope (EFM) Magnetic Force Microscope (MFM) Scanning Tunneling Microscope (STM) Near-field Scanning Optical Microscope (SNOM)

History The scanning tunneling microscope was developed at IBM Zürich in 1981 by Gerd Binning and Heinrich Rohrer who shared the Nobel Prize for physics in 1986 because of the microscope. Gerd Binning Heinrich Rohrer

Scanning Tunneling Microscope (STM) The STM is an electron microscope that uses a single atom tip to attain atomic resolution.

SPM Systems Piezoelectric Scanner

General Overview An extremely fine conducting probe is held about an atom’s diameter from the sample. Electrons tunnel between the surface and the tip, producing an electrical signal. While it slowly scans across the surface, the tip is raised and lowered in order to keep the signal constant and maintain the distance. This enables it to follow even the smallest details of the surface it is scanning.

The Tip As we will see later, is very important that the tip of the probe be a single atom. Tungsten is commonly used because you can use Electro-chemical etching techniques to create very sharp tips like the one above.

Quantum Tunneling The second tip shown above is recessed by about two atoms and thus carries about a million times less current. That is why we want such a fine tip. If we can get a single atom at the tip, the vast majority of the current will run through it and thus give us atomic resolution.

Note A STM does not measure nuclear position directly. Rather it measures the electron density clouds on the surface of the sample. In some cases, the electron clouds represent the atom locations pretty well, but not always.

Converse Piezoelectricity Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. When you apply an electric field to a piezoelectric crystal, the crystal distorts. This is known as converse piezoelectricity. The distortions of a piezo is usually on the order of micrometers, which is in the scale needed to keep the tip of the STM a couple Angstroms from the surface. Electric Field Pizos The tip

Advantages of Scanning Probe Microscopy The resolution of the microscopes Create small structures nanolithography Do not require a partial vacuum Disadvantages of Scanning Probe Microscopy The detailed shape of the scanning tip Slower in acquiring images The maximum image size

Scanning Modes STM Constant Current Mode

STM Constant Height Mode

System Components Mechanical Parts Electronics Parts Computer + software

Needle replacement Needle type Platinum-iridium (PtIr) Tungsten tips Gold Needle preparation Electrochemical etching Mechanical shearing

System Software Execution

Sample preparation

ZnO Nanoparticles around 6.5-8nm www.natsyco.com

Gold Nano crystals 6-14nm www.natsyco.com

Gold Nano crystals 6-14nm

Gold Nano crystals 6-14nm www.natsyco.com

Calibration

Etching of atoms and molecules from the surface of gold (100x100nm) by our STM system (a step for Nanorobotics)

Atomic resolution of graphite 4x4x 0.2nm

Atomic resolution of graphite

References Pooria Gill, Bijan Ranjbar, Reza Saber. Scanning Tunneling Microscopy of Cauliflower-like DNA Nanostructures Synthesized by Loop-mediated Isothermal Amplification. IET Nanobiotechnology 2011; 5 (1), 8-13. Reza Saber, Saeed Sarkar, Pooria Gill, Behzad Nazari, Faramarz Faridani. High Resolution Imaging of IgG and IgM Molecules by Scanning Tunneling Microscopy in Air Condition. Scientia Iranica (Transaction F: Nanotechnology) 2011; 18 (6), 1643–1646. M.Q. Li. Scanning probemicroscopy (STM=AFM) and applications in biology, Appl. Phys. A 68, 255–258 (1999). Errez Shapir et al., High-Resolution STM Imaging of Novel Single G4-DNA Molecules, J. Phys. Chem. B, Vol. 112, No. 31, 2008. D. P. ALLISON. Immobilization of DNA for scanning probe microscopy, Proc. Nadl. Acad. Sci. USA, Vol. 89, pp. 10129-10133, November 1992. Hiroyuki Tanaka. Visualization of the Detailed Structure of Plasmid DNA, J. Phys. Chem. B 16788 2008, 112, 16788–16792. Hiroyuki Tanaka. High-resolution scanning tunneling microscopy imaging of DNA molecules on Cu(111) surfaces, Surface Science 432 (1999) L611–L616. Handbook of microscopy for nanotechnology / edited by Nan Yao. Zhong Lin Wang. 2005 Kluwer Academic Publishers. Scanning probe microscopes : applications in science and technology / K.S. Birdi. 2003 by CRC Press LLC. SCANNING PROBE MICROSCOPY, 2007 Springer Science+Business Media, LLC.

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